There has been a conventional air conditioner which is so composed that an indoor unit is connected to an outdoor unit in which a compressor, a four-way selector valve, a thermal-source-side heat exchanger, a motor-operated expansion valve and a receiver are sequentially connected, as disclosed in Japanese Patent Application Laid-Open Gazette No. 4-344085. The air conditioner performs defrosting operation when a fin of the thermal-source-side heat exchanger is frosted in heating operation.
Further, the defrosting operation is executed in a cooling cycle with a non-shown motor-operated expansion valve of the indoor unit and the motor-operated expansion valve of the outdoor unit fully opened together.
Problems to be solved
However since the above air conditioner is provided with an accumulator on a suction side of the compressor in order to prevent operation in wet condition of the compressor, the motor-operated expansion valves are fully opened in the defrosting operation so that operation performance is decreased due to pressure loss at the accumulator.
If the accumulator is not provided to solve the above problem, since the defrosting operation with the motor-operated expansion valves fully opened, this causes liquid refrigerant condensed by the thermal-source-side heat exchanger to store in the receiver in the case of heavy frost, low open-air temperature or short refrigerant piping. Thus, an amount of heat required for defrosting is lacked so that the liquid refrigerant in the receiver turns back to the compressor. This invites operation in wet condition of the compressor, so that the compressor is under stress. As a result, the reliability of the compressor is reduced.
In view of the foregoing problems, this invention has been made. An object of this invention is to enhance operation performance without any accumulator while avoiding the compressor from operating in wet condition in defrosting operation.